A prior art branching device of this type comprises a main body having an input terminal and an output terminal, each for connecting a trunk cable, and a branch body having a branch terminal for connecting a branch cable. The main body and the branch body are each provided with a pair of connecting terminals, one pair detachable from the other pair, for delivering a high-frequency signal from the main body to the branch body. The main body contains a branching element for passing the high-frequency signal input at the input terminal through to the output terminal while diverting a portion of the high-frequency signal for supply to the connecting terminals on the main body. The branch body contains a signal sendout circuit for sending the high-frequency signal input at the connecting terminals on the branch body out to the branch terminal. (Refer, for example, to Japanese Patent Unexamined Publication No. 63-209316).
With this kind of branching device, when a subscriber desires to receive a high-frequency signal, for example, a television signal, he can receive the television signal via the branch terminal and view the desired program. When the number of subscribers increases, the branch body is replaced by a branch body equipped with a larger number of branch terminals, thus increasing the number of branch terminals and allowing distribution of television signals to the increased number of subscribers. Work involved with this addition is easy since it can be accomplished by simply replacing the branch body while keeping the main body connected in the trunk cable. Furthermore, since the output of the television signal from the output terminal on the main body can be continued during the work, the work for the addition can be done without causing interruption in signal transmission to the subscribers who are receiving the television signal off the trunk cable connected on the output side.
In the above prior art high-frequency signal branching device, however, if the branch body is replaced, the branching element provided in the main body continues to be used. This means that the level of signal to be supplied to the branch body is the same as before. As a result, the level at each branch terminal drops in proportion to the increase in the number of branch terminals. This has lead to the problem that if the distance to a new subscriber, and hence the length of the branch cable to that subscriber, is long, signal loss increases while the television signal is being transmitted through the branch cable, resulting in an insufficient television signal level, and hence picture quality degradation, in the subscriber's home. Furthermore, when the number of subscribers to be added is very large, a significant loss occurs when branching the high-frequency signal into a large number of branch terminals in the branch body; this has caused the problem that the television signal level at each branch terminal is insufficient and picture quality degrades at television sets receiving television signals via these branch terminals.
It is an object of the present invention to provide a high-frequency signal branching device that can tap a high-frequency signal and output it at a branch terminal for reception when it is desired to receive the high-frequency signal.
Another object is to permit the number of branch terminals to be increased to provide for an increase in the number of subscribers to high-frequency signal reception and to ensure that the signal can be delivered via each branch terminal to each of the subscribers.
Another object is to make it easy to increase the number of branch terminals.
Another object is to provide the necessary and sufficient level of signal to every subscriber when making provision to distribute the high-frequency signal to the increased number of subscribers.
Another object is to make it possible to do the work to increase the number of branch terminals while allowing the output of the high-frequency signal from the output terminal to be continued during the work so that no interruptions are caused in the signal transmission to subscribers receiving the high-frequency signal off the trunk cable connected on the output side.
More specifically, the object is to provide a high-frequency signal branching device that can allow the output side to continue to supply the signal without causing momentary interruptions or level drops in the signal (without causing momentary signal interruptions or voltage drops) during the work whether the signal is an analog signal or a digital signal, and that can continue to supply a constant level of signal to the output side without causing variations in the level while the work to increase the number of branch terminals is in progress.
Another object is to provide a high-frequency branching device that permits creation of specifications optimum for each subscriber premises by making arrangements so that the problem of providing branch terminals in a quantity appropriate to the number of subscribers and the problem of supplying the necessary and sufficient level of signal to the branch terminals can be addressed individually when making provision to distribute the high-frequency signal to the increased number of subscribers.
More specifically, the object is to provide a high-frequency signal branching device that allows only the number of branch terminals on the branch body to be increased while keeping the branching circuit in the branch body intact and thus not changing its insertion loss, or that permits work to be done to change only the coupling loss by replacing the branching circuit in the branch body without removing the branch cables connected to the branch terminals on the branch body.
Other objects and advantages will become more apparent from the drawings and the description given hereinafter with reference to the drawings.